This invention relates to an information processing system which is capable of processing each instruction by the use of a microprogram and which is capable of judging a branch condition in the microprogram.
In a conventional information processing system of the type described, each program instruction or macroinstruction in a program is very often processed by the use of a plurality of microinstructions which are memorized in a control memory having a plurality of addresses. It is well known that branch microinstructions are included in such microinstructions so as to determine branch conditions. For this purpose, each of the branch microinstructions includes a branch condition selection area or field composed of a predetermined number of bits which will be called branch condition bits. Such branch condition bits are used as a zero detection signal representative of zero detection of a calculation result, a sign bit signal, a carry signal, an overflow signal, a wide variety of flags, and a mode signal indicative of various modes. Under the circumstances, the branch condition selection area in each branch microinstruction should have a bit number determined by the number of the branch conditions. Accordingly, the bit number of the branch condition selection area increases with an increase of the number of the branch conditions. This results in an increase of a memory capacity of the control memory. Thus, an amount of hardware must be inevitably increased with an increase of the branch conditions.